题目内容
如图所示,足够长的光滑U型导轨宽度为L,其所在平面与水平面的夹角为
,上端连接一个阻值为R的电阻,置于磁感应强度大小为B,方向垂直于导轨平面向上的匀强磁场中,今有一质量为
、有效电阻
的金属杆沿框架由静止下滑,设磁场区域无限大,当金属杆下滑达到最大速度时,运动的位移为
,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250043518002532.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351753191.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351753204.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351769182.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351785191.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250043518002532.png)
A.金属杆下滑的最大速度![]() |
B.在此过程中电阻R产生的焦耳热为![]() |
C.在此过程中电阻R产生的焦耳热为![]() |
D.在此过程中流过电阻R的电量为![]() |
B
感应电动势为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351878299.png)
感应电流为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351894338.png)
安培力为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351909550.png)
根据平恒条件得
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351925442.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351941659.png)
由能量守恒定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351956643.png)
又因
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351972459.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004351987863.png)
由法拉第电磁感应定律得通过R的电量为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004352003603.png)
所以选项B正确
![](http://thumb2018.1010pic.com/images/loading.gif)
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